MPEG audio decoding system with subframe input buffering

Abstract

A Motion Picture Experts Group (MPEG) video/audio data bitstream comprises frames of encoded audio data, each of which includes a plurality of integrally encoded subframes, which are decoded by an audio decoder for presentation. An input buffer arrangement includes first and second buffer memories which each have a capacity to store one subframe. The first and second buffer memories are used alternatingly, with one storing a subframe of input data while another subframe is being read out of the other. A third buffer memory, which has a capacity to store at least one subframe, is provided upstream of the first and second buffer memories to prevent the first and second buffer memories from overflowing or underflowing.

I claim: 
     
       1. A decoding system for decoding a data bitstream including frames of data, each frame including a plurality of subframes of integrally encoded data, comprising: a first buffer memory having a capacity for storing at least one subframe;   a second buffer memory having a capacity for storing at least one subframe;   controller means for alternatingly storing subframes in the first buffer memory and the second buffer memory; and   decoding means for reading out and decoding a subframe from the first buffer memory while the controller means stores a subframe in the second buffer memory, and reading and decoding a subframe from the second buffer while a subframe is being stored in the first buffer memory.   
     
     
       2. A system as in claim 1, further comprising a third buffer memory disposed upstream of the first and second buffer memories. 
     
     
       3. A system as in claim 2, in which the third buffer memory has a capacity for storing at least one subframe. 
     
     
       4. A system as in claim 1, in which the controller means comprises: computing means for computing a number of bits in one subframe;   counting means for counting bits of said bitstream; and   toggling means for toggling the first buffer memory between a read mode and a write mode and toggling the second buffer memory between said write mode and said read mode respectively in response to the counter means counting said number of bits.   
     
     
       5. A system as in claim 4, in which: the counting means loads said number of bits from the computing means in response to a reset condition, and is decremented by counting said bits; and   the toggling means toggles the first and second buffer memories in response to the counting means being decremented to zero.   
     
     
       6. A system as in claim 5, in which each of the first and second buffer memories generates said reset condition in response to a subframe being read out thereof by the decoding means. 
     
     
       7. A system as in claim 5, in which the decoding means generates said reset condition in response to completion of decoding a subframe. 
     
     
       8. A system as in claim 4, in which: each frame of data further includes information indicating said number of bits; and   the computing means computes said number of bits from said information.   
     
     
       9. A system as in claim 4, in which: said bitstream is an MPEG bitstream, comprising a header for each frame including audio subband allocation data; and   the computing means computes said number of bits from said subband allocation data.   
     
     
       10. A system as in claim 9, in which the computing means comprises: header decoding means for decoding said header to obtain said subband allocation data; and   summing means for summing said subband allocation data to obtain said number of bits.   
     
     
       11. A system as in claim 1, in which the first and second buffer memories each have a capacity for storing no more than one subframe. 
     
     
       12. A method of decoding an MPEG bitstream including frames of data, each frame including a plurality of subframes of integrally encoded audio subband sample data, comprising the steps of: (a) providing a first buffer memory having a capacity for storing at least one subframe;   (b) providing a second buffer memory having a capacity for storing at least one subframe;   (c) alternatingly storing substantially one subframe at a time in the first buffer memory and the second buffer memory; and   (d) reading out and decoding a subframe from the first buffer memory while a subframe is being stored in the second buffer memory, and reading and decoding a subframe from the second buffer while a subframe is being stored in the first buffer memory.   
     
     
       13. A method as in claim 12, further comprising the step, performed prior to step (c), of: (e) providing a third buffer memory upstream of the first and second buffer memories; and   (f) using the third buffer memory to accumulate said data.   
     
     
       14. A method as in claim 13, in which step (e) comprises providing the third buffer memory as having a capacity for storing at least one subframe. 
     
     
       15. A method as in claim 12, in which step (c) comprises the substeps of: (e) computing a number of bits in one subframe;   (f) counting bits of said bitstream; and   (g) toggling the first buffer memory between a read mode and a write mode and toggling the second buffer memory between said write mode and said read mode respectively after said number of bits has been counted in step (f).   
     
     
       16. A method as in claim 15, in which: each frame of data further includes information indicating said number of bits; and   step (e) comprises computing said number of bits from said information.   
     
     
       17. A method as in claim 15, in which: each frame comprises a header including subband allocation data; and   step (e) comprises computing said number of bits from said subband allocation data.   
     
     
       18. A method as in claim 17, in which step (e) comprises the substeps of: (h) decoding said header to obtain said subband allocation data; and   (i) summing said subband allocation data to obtain said number of bits.   
     
     
       19. A method as in claim 12, in which: step (a) comprises providing a first buffer memory having a capacity for storing no more than one subframe; and   step (b) comprises providing a second buffer memory having a capacity for storing substantially one subframe.   
     
     
       20. A decoding system for decoding an MPEG input data bitstream including frames of data, each frame including a plurality of subframes of integrally encoded audio subband sample data, comprising: a first buffer memory having a capacity for storing at least one subframe;   a second buffer memory having a capacity for storing at least one subframe;   a third buffer memory disposed upstream of the first and second buffer memories;   controller means for alternatingly storing subframes in the first buffer memory and the second buffer memory; and   decoding means for reading out and decoding a subframe from the first buffer memory while the controller means stores another subframe in the second buffer memory.   
     
     
       21. A system as in claim 20, in which the third buffer memory has a capacity for storing at least one subframe. 
     
     
       22. A system as in claim 20, in which the controller means comprises: computing means for computing a number of bits in one subframe;   counting means for counting bits of said bitstream; and   toggling means for toggling the first buffer memory between a read mode and a write mode and toggling the second buffer memory between said write mode and said read mode respectively in response to the counter means counting said number of bits.   
     
     
       23. A system as in claim 22, in which: the counting means loads said number of bits from the computing means in response to a reset condition, and is decremented by counting said bits; and   the toggling means toggles the first and second buffer memories in response to the counting means being decremented to zero.   
     
     
       24. A system as in claim 23, in which each of the first and second buffer memories generates said reset condition in response to a subframe being read out thereof by the decoding means. 
     
     
       25. A system as in claim 24, in which: said bitstream comprises a header for each frame including subband allocation data; and   the computing means computes said number of bits from said subband allocation data.   
     
     
       26. A system as in claim 25, in which the computing means comprises: header decoding means for decoding said header to obtain said subband allocation data; and   summing means for summing said subband allocation data to obtain said number of bits.   
     
     
       27. A system as in claim 23, in which the decoding means generates said reset condition in response to completion of decoding a subframe. 
     
     
       28. A system as in claim 22, in which: each frame of data further includes information indicating said number of bits; and   the computing means computes said number of bits from said information.   
     
     
       29. A system as in claim 20, in which the first and second buffer memories each have a capacity for storing no more than one subframe.